The aim of this project is to investigate the effects of stimulus intensity on neural responses in the auditory system and to test a number of existing hypotheses with regard to intensity coding. Special emphasis is on the roles of time and space in determining and modifying or adapting the coding mechanisms. Towards this end we propose to measure functional relationships between stimulus intensity and neural response, to study their implications for psychophysical performance, and to investigate the mechanisms underlying these relationships. Results will be compared , inorder to evaluate similarities and differences between the peripheral auditory and tactile systems with respect to the general roles of intensity level, time, and space in encoding intensity. The experiments involve effects of intensity on the magnitude and variability of neural responses, the alteration of these effects by prior and ongoing background stimulation, and by structural modification. A variety of approaches are proposed to reveal various aspects of the encoding mechanisms and develop a comprehensive description of intensity coding. Auditory-nerve studies in anesthetized gerbils and chinchillas involve the distribution of responses with intensity and time across the subpopupulations of low and high spontaneous-rate fibers as the spatial distributions and temporal variability produces by tones and noise with various spectral distributions. The role of cochlear input and its possible modification by efferent influences are also to be determined. Compound responses and cochlear emissions will be obtained in humans for comparison to properties revealed in the laboratory animals, and to help evaluate the appropriateness of acute animal experiments for modeling the human system. Results will be utilized in a comparative analysis of the psychophysiological functioning of the auditory and tactile systems. This should lead to an improved understanding of their functioning in normal and pathological conditions and provide insights into designing methods for ameliorating sensory deficits.